The present invention relates to a three-port valve used to switch between various fluids, for example, to switch between a vacuum pump, a vacuum chamber, and the atmosphere.
FIG. 4 shows a conventional three-port valve (more specifically, a three-port solenoid valve). The three-port valve has a body part 11 and a solenoid part 12. The body part 11 and the solenoid part 12 are connected together through an annular spacer 13. A retainer 14 is secured to the bottom of the body part 11. The solenoid part 12 has a fixed iron core 16 at the upper end thereof. In a top plan view, the fixed iron core 16 lies in the center of the solenoid part 12. A guide cylinder 17 is connected to the outer surface of the fixed iron core 16 and extends downward. A pair of upper and lower magnetic flange members 18 and 19 and a bobbin 20 are connected to the outer periphery of the guide cylinder 17. A solenoid 21 is fitted on the bobbin 20. The outer peripheries of the solenoid 21 and bobbin 20 are protected by cover members 22 and 23 and frame members 24 and 25. The outer sides of the frame members 24 and 25 are secured by a body 26 made of a synthetic resin material. The frame members 24 and 25 and the annular spacer 13 are connected together through a coned disc spring 27. The lower end portion of the guide cylinder 17 is engaged with the lower end portion of the spacer 13. A plate member 28, together with a snap ring 29, is engaged in an upper annular groove provided in the upper end portion of the fixed iron core 16, thereby positioning the synthetic resin body 26.
The body part 11 includes a body member 32. The body member 32 has an upper cylindrical portion 33 projecting upward. A cylindrical portion 34 projects from one side (left-hand side as viewed in FIG. 4) of the body member 32. The cylindrical portion 34 will be hereinafter referred to as "left cylindrical portion 34". A cylindrical portion 35 projects from the other side (right-hand side as viewed in FIG. 4) of the body member 32. The cylindrical portion 35 will be hereinafter referred to as "right cylindrical portion 35". The body member 32 further has therein a second port block 37 provided with a second port 47. The upper cylindrical portion 33, the left cylindrical portion 34, the right cylindrical portion 35, and the second port block 37 are integrally formed as one unit. A central bore 39 vertically extends through the central portion of the body member 32. The second port block 37 lies across the central bore 39. The upper end of the central bore 39 is communicated with the inside of the upper cylindrical portion 33. The lower end of the central bore 39 is fitted with an annular projection 41 of the retainer 14. Thus, a central valve chamber 42 is formed in the central bore 39. A communicating passage 53 having an L-shaped cross-sectional configuration is formed in the retainer 14. The communicating passage 53 opens at one end thereof on one side of the retainer 14 and at the other end thereof on the top of the retainer 14. The one end portion of the communicating passage 53 is closed with a stopper member 44. A first port 45 is formed in the right cylindrical portion 35. A third port 46 is formed in the left cylindrical portion 34. The first port 45 and the communicating passage 53 are communicated with each other by a vertically extending communicating passage 52. An annularly projecting first valve seat 55 is formed at the center of the wall of the retainer 14 inside the annular projection 41. A first passage 49 extends through the first valve seat 55 to provide communication between the communicating passage 53 and the central valve chamber 42. An annularly projecting second valve seat 56 is formed at the center of the lower end of the second port block 37. A second passage 51 extends through the second valve seat 56 to provide communication between the second port 47 and the central valve chamber 42. As illustrated in the figure, the first valve seat 55 and the second valve seat 56 are disposed at respective positions facing opposite to each other on the same axis, and alternately closed by a valve body 40 which is caused to perform reciprocating motion. The third port 46 and the central valve chamber 42 are communicated with each other by a third passage 50. The third passage 50 opens to the one side of the central bore 39.
FIG. 3(d) is an enlarged perspective view of a support 58 for supporting the valve body 40. As shown in FIGS. 4 and 3(d), the valve body 40 is fitted in the central bore of a ring portion 59 of the support 58. Two connecting rods 60 are secured to two opposite sides, respectively, of a vertical flange of the ring portion 59. The connecting rods 60 extend upward. Before the retainer 14 is connected, the connecting rods 60 and the ring portion 59, which constitute the support 58, are inserted into the central bore 39 of the body member 32 from the lower side such that the connecting rods 60 extend through the space between the second port block 37 and the central bore 39. A seat spring 63 is inserted into the central bore 39 from the upper side and placed on the top of the second port block 37. Upper portions of the connecting rods 60 are fitted into respective cut portions provided in the outer peripheral portion of an upper plate 61, thereby securing the connecting rods 60. Thus, the support 58 is constructed. The upper end portion of the connecting rods 60 project from the top of the upper plate 61, and the upper ends of the connecting rods 60 abut on the lower end of a movable iron core 64 (described later). The movable iron core 64 has a central hole opening on the upper end thereof, and an armature spring 65 is fitted in the central hole. The movable iron core 64 is inserted into the guide cylinder 17 of the solenoid part 12 from the lower side and reciprocatably fitted therein. The upper end of the armature spring 65 is engaged with the lower end portion of the fixed iron core 16. In a state where the solenoid part 12 and the spacer 13 are connected together, the outer small-diameter portion of the spacer 13 is fitted into the bore of the upper cylindrical portion 33 of the body part 11, thereby securing the body part 11 and the solenoid part 12. Thus, the three-port valve shown in FIG. 4 is obtained.
The armature spring 65 and the seat spring 63 act so as to push each other. Downward resilient force from the spring 65 is transmitted to the valve body 40 through the movable iron core 64 and the support 58. Upward resilient force from the seat spring 63 is transmitted to both the valve body 40 and the movable iron core 64 through the support 58. The resilient force of the armature spring 65 is set greater than the resilient force of the seat spring 63. Thus, when the solenoid 21 is deenergized, the valve body 40 is biased downwardly, as shown in the figure. As a result, the lower seal surface of the valve body 40 is placed in close contact with the first valve seat 55, while the upper seal surface of the valve body 40 is separate from the second valve seat 56. When the solenoid 21 is energized, the movable iron core 64 is pulled upwardly against the resilient force of the armature spring 65, causing the upper end of the movable iron core 64 to contact the lower end of the fixed iron core 16. Accordingly, both the support 58 and the valve body 40 are biased upwardly by the resilient force of the seat spring 63. As a result, the upper seal surface of the valve body 40 comes in close contact with the second valve seat 56, while the lower seal surface of the valve body 40 separates from the first valve seat 55. In order for the upper seal surface of the valve body 40 to come in close contact with the second valve seat 56 to surely close the second passage 51 when the solenoid 21 is energized, the stroke VS of the valve body 40 is set smaller than the stroke AS of the movable iron core 64. Regardless of the strokes VS and AS thus set, when the solenoid 21 is deenergized, the lower seal surface of the valve body 40 comes in close contact with the first valve seat 55.